1. Field of the Invention
This invention relates generally to a low-noise, broad band switch and phase shifter and, more particularly, to a monolithic microwave and millimeter wave balanced, low-noise, broad band switch, switch and phase shifter that has particular application as a balanced switching low-noise amplifier.
2. Discussion of the Related Art
High performance, low-noise solid state switches and phase shifters are important control elements for controlling signal flow in high frequency circuit applications. One particular application exists for such a switch and phase shifter in microwave control circuits that are part of a phased-array or focal plane array antenna system. Typical focal plane array or phased-array antenna systems will incorporate a large number of antenna elements that either passively or actively detect radiation from a scene. Each antenna element may include a balanced switching, low-noise amplifier (BSLNA) that is selectively switched on and off to allow RF signals sensed by the particular antenna element to be sent to a detector device, such as a diode, that converts the RF signals to corresponding DC level signals. Currently, such BSLNAs are generally monolithically integrated into monolithic microwave integrated circuits or monolithic millimeter wave integrated circuits (MMICs) along with the antenna array and associated processing circuitry.
Different switching and amplifying elements have been previously used to provide low-noise switching and phase shifting of the type discussed above. Most microwave and millimeter wave switches incorporate PIN diodes or field effect transistors (FETs) in series, shunt, or series-shunt configurations. Although the switches using PIN diodes have demonstrated great performance, they are not monolithically compatible with other FET devices in MMICs. Additionally, PIN diode switches consume more DC power, and require complicated bias circuitry that usually degrades switching speeds. For a discussion of PIN switches in this context, see for example Bellantoni, J. P. et al., "A Monolithic High Power Ka Band PIN Switch," IEEE Microwave and Millimeter-Wave Monolithic Circuit Symposium, May, 1989, pp. 47-53.
On the other hand, FET switches, such as metal semiconductor field effect transistor (MESFET) switches or high electron mobility transistor (HEMT) switches, often show a higher insertion loss than PIN switches. The high insertion loss degrades receiver noise performance and transmitter efficiency especially a high frequency. Further, the parasitic source-drain capacitance of an FET at pinch-off limits the isolation and band width of the FET switches. This adverse parasitic capacitance is further increased with increasing frequency, in particular millimeter wavelength frequencies. For a discussion of FET switches in this context, see for example Schindler, Manfred et al., "DC-40 GHz and 20-40 GHz MMIC SPDT Switches," IEEE Trans. on Microwave Theory and Techniques, Vol. 35, 1987, pp. 1486-1493.
Since phase shifters typically incorporate one or more switches of this type to change the phase difference between input and output signals, the same problems described above also exist for these types of phase shifters.
A need exists for a high performance switch and phase shifter especially suitable for MMIC applications that provides greater device performance than known switch and phase shifters that incorporate PIN diodes or FETs switches in series, shunt, or series-shunt configurations. It is therefore an object of the present invention to provide such a switch and phase shifter.